THIAZOLES, in organic chemistry, a series of heterocyclic compounds containing the grouping shown below; the re-
placeable hydrogen atoms in which are designated a, i and µ. They are prepared by condensing thio-amides with a-haloid
ketones or aldehydes, the thio-amide reacting as the tautomeric thio-imino acid. Amino derivatives similarly result from thio-ureas and a-haloid ketones; the oxy derivatives from a-sulphocyanoketones by the action of caustic alkali; and the carboxylic acids from chloro-aceto-acetic ester, &c. and thioamides. The thiazoles are somewhat basic in character, and combine with the alkyl iodides to form thiazolium iodides.
Dihydrothiazoles, or thiazolines, are obtained by condensing ethylene dibromides with thio-amides; by the action of $-haloid alkylamines on thio-amides (S. Gabriel, Ber., 1891, 24, p. 783; 1896, 29, p. 2610) ; and by the action of phosphorus pentasulphide on acyl-p-bromalkylamides (A. Salomon, Ber., 1893, 26, p. 1328). They are much less stable than the thiazoles. The benzothiazoles are a series of weak bases formed by condensing carboxylic acids with ortho-aminothiophenols (A. W Hofmann, Ber., 188o, 13, p. 1224), by heating the acid anilides with sulphur or by the oxidation of thio-anilides. On fusion with caustic alkalis they decompose into their constituent aminothiophenol and acid. Derivatives of this group are important as substantive cotton dye-stuffs.